1. Field of the Invention
This invention relates generally to the field of semiconductor processing technology. More specifically, this invention relates to the conditioning and cleaning of polishing pads used in the substrate polishing and planarization process of semiconductor manufacturing.
2. Description of the Related Art
During the manufacturing process of an integrated circuit, a semiconductor wafer is often polished to remove unwanted materials on the surface of the wafer. The polishing or planarization process can also remove a layer or a partial layer comprised of a material (usually of thin film), such as dielectric, metal, or polysilicon, deposited on the surface of a semiconductor wafer in order to form the necessary interconnects, insulation, and various components of the integrated circuit.
One such process involves polishing the substrate on a polishing pad. One polishing process is commonly referred to as Chemical-Mechanical Polishing (CMP). In a typical arrangement, a substrate is supported by a carrier which presses the substrate against the surface of a moving polishing pad. The polishing process may take place in the presence of a polishing slurry, water (with or without some amount of suitable chemical), or without any such agent. However, with CMP a polishing slurry is generally utilized. The polishing process continues in this manner until the desired surface of the substrate is planarized or in some cases completely removed.
During the polishing process, the properties of the polishing pad can change. Slurry particles and polishing byproducts accumulate on the surface of the pad. Polishing byproducts and morphology changes on the pad surface affect the properties of the polishing pad and cause the polishing pad to suffer from a reduction in both its polishing rate and performance uniformity. Pad conditioning restores the polishing pad's properties by re-abrading or otherwise restoring the surface of the polishing pad. This conditioning process enables the pad to maintain a stable removal rate while polishing a substrate or planarizing a deposited layer and lessens the impact of pad degradation on the quality of the polished substrate.
During the conditioning process, a conditioner (also referred to as an end effector) used to recondition the polishing pad's surface comes into contact with the pad and re-abrades the pad's surface. The type of conditioner used depends on the pad type. For example, hard polishing pads, typically constructed of synthetic polymers such as polyurethane, require the conditioner to be made of a very hard material, such as diamond, serrated steel, or ceramic bits, to recondition the pad. Intermediate polishing pads with extended fibers require a softer material, often a brush with stiff bristles, to recondition the pad. Meanwhile, soft polishing pads, such as those made of felt, are best conditioned by a soft bristle brush or a pressurized spray.
Pad conditioning devices known in the prior art employ a single conditioner, conditioning means, or end effector brought into contact with the polishing pad. Generally, the selected conditioner is designed to recondition a specific type of pad surface. For example, U.S. Pat. No. 5,154,021 raises flattened pad fibers with a downward directed stream of air. This method works best on intermediate pad surfaces with longer pad fibers, but is not as successful on harder pad surfaces such as polyurethane. On the other hand, U.S. Pat. Nos. 5,486,131 and 5,547,417 recondition the pad surface using cutting means and a grooved block fitted with diamond tips, respectively. These methods are well suited for harder polishing pads like polyurethane, but would be too rough for a more intermediate pad surface. Thus, every time the type of polishing pad on the polishing machine changes, the conditioning mechanism must also be replaced with a conditioner having properties necessary to condition the new type of pad. This requires the polishing machine user to maintain several different types of conditioning devices, one for each different type of polishing pad used. Also, time is required to change the conditioner.
Similarly, the prior art does not allow for complex conditioning of a polishing pad. Complex conditioning involves a more controlled and varied conditioning than is currently possible. For example, the polishing pad of an orbital polishing machine often becomes more worn along the track the wafer follows during polishing. Conditioning of the wafer track may require reabrasion of the pad surface with a diamond cutting means followed by brushing off the pad surface with a soft bristle. In contrast, the area outside the wafer track often merely needs to be brushed with a soft bristle or rinsed. This type of varied conditioning treatment is not possible when only one conditioning means is available for use with each polishing apparatus.
In addition to only being able to condition a single type of pad, the prior art conditioners are utilized to re-abrade the polishing pad. A conditioner having an independent means for cleaning the re-abraded pad would be desirable. It would also be advantageous to simultaneously or sequentially re-abrade and clean the pad without stopping the polishing process to change the conditioning medium.